Flight calculator



Jan. E. c. HOKANSON 2,339,222

- v FLIGHT CALCULATOR Filed Feb. 28, 1941 2 Sheets-Sheet l FIG. 3

Jan. 11, 1944.. E. c. HOKANSON FLIGHT CALCULATOR I 2 Sheets-Sheet 2 Filed Feb'. 28 1941 FIG. 5

l I( mun (m E u h 03 um? ME 4| I INVENTOR Patented Jan. 11 1944 UNITED STATES PATENT orrlcs FLIGHT CALCULATOR Evert Carl Hokanson, Arlington County, Va., as-

signor to Aeronav Instrument Company, New York, N. Y., a proprietorship of New York, N. Y.

Application February 28, 1941, Serial No. 381,145

6 Claims.

This invention relates to simplification and improvements of mechanical calculating and computing devices, more particularly to calculating and computing instruments of the portable type adapted to make calculations and computations pertaining to air navigation.

Air navigation by means of dead reckoning the true heading), (6) wind velocity and ('7) true wind direction. By proper use and combinations of these variables, that is, by dead reckoning, it

is possible to determine or to predetermine a new position from a known postion.

In every case a certain number of the aforementioned variables are known and the others are unknown but can be calculated or computed trigonometrically, vectorially or mathematically. My invention provides simplified means for rapidly determining the unknown variables from the the known variables as well as presenting agraphic picture of the relation between certain variaables, namely true airspeed, true heading, ground speed, true course, wind velocity, true wind direction and drift.

The importance of solving air navigation problems accurately and quickly is recognized by pilots and all persons charged with the responsibility for aircraft flights, particularly when weather conditions are such that it is necessary to rely on the instruments in the aircraft (instrument flyingrather than by visual observation of the terrain over which the flight is being made. Changing conditions. such as a change in wind direction and velocity, which may be encountered during a flight, requires the solving of another air navigational problem by dead reckoning, in order to determine ,the.new course and time of arrival. This is readily accomplished on large aircraft where one man is the navigator having a navigators table, maps, charts, straight edges, scales, protractors, etc., at his disposal. On small aircraft, where one man must be sufficient unto himself, it is necessary that he have reliable aids which he can operate while he is flying th aircraft. An attempt has been made to supply this need by the use or various mechanical devices, but these have been either too cumbersome, heavy and expensive or too complicated and thereby requiring the memorizing of definite procedures which may be forgotten in the stress of an emergency. Some of these mechanical navigational devices now in use have proved satisfactory for professional pilots but have not supplied the need of the private pilot who only makes an occasional crosscountry flight.

The general object of my invention is to supply the need for a mechanical air navigational calculating device. More specifically to supply the private pilots need for a flight calculator.

It is also the object of my invention to provide a flight calculator which issimple, understand-' able, and so constructed that the elements form a graphic picture of the basic wind triangle as taught in all aviation ground schools.

Another object of my invention is to provide a flight calculator for the pivate pilot which combines in one instrument simplified means for calculating all the essential factors involved in air navigation problems. i

A further object of my invention is to provide a flight, calculator of rugged construction, light in weight, relatively inexpensive and of a'size which can be easily carried in an average size coat pocket and thus be readily available at all times both prior and during a flight.

These objects are attained in a mechanical navigationalv and computing device constructed ac- I the calculator.

cording to my invention. The accompanying drawings illustrate the principle and the simplicity of construction of the invention.

Figure 1 shows the navigation side of the calculator. Figure 2 shows a side view of the calculator. Figure 3 shows a sectional view of the calculator as developed on the line 33 of Figure 1. Figure 4 shows the flight factor side of Figure 5' shows a sectional view developed on the line 55 of Figure 4. Figure 6 shows a variation of the navigation side of the calculator as illustrated in Figure 1. .All markings on the surfaces of the component parts of the flight calculator are printed,- stamped, engraved or marked by some similar means.

A general description will first be given of the navigational side of the flight calculator as shown inFigure 1. The base I0 of the device is a flat member made of opaque material which is relatively thin and approximately four to five times as long as it is wide. Near one end of the base III is a pivot H by means of which a flat circular stops 32 disc or wind dial II is rotatably mounted on the base i 0. The wind dial II is a combination compass card and graduated wind rose made of an opaque material, the radial lines 22 correspond to wind directions, the circular lines 23 correspond to wind velocities and the graduations 2| adjacent the outer edge of the dial correspond to the graduations of a compass card. These graduations 2| are used for both courses and wind directions so that they maintain fixed relations to on another at all times. The base ID has an arcuate scale 20 and a true course index l9 which cooperate with the outer graduations 2| of the wind dial H. The slide assembly I3 comprises an arm M, a slide member 15 and a pivot IS. The arm I4 has an arcuate scale 25 at one end which corresponds to drift angle, a linear scale-24 which corresponds to true airspeed, is made of a transparent material and is mounted by means of the pivot Hi to slide member B5 in order to obtain angular movement for a drift indication. The slide member i5 is made of a transparent material, is slidably mounted on the base ID, has flanged portions I! which engage the sides of the base In in a manner to permit reciprocal movement of the slide assembly I3 over the base l0, has an index 26 which cooperates with the arcuate scale 25 to indicate drift angle and has an index 21 which cooperates with the linear scale 28 on the base I to indicate ground speed. The washer I8 spaces the arm l4 from the slide member I5. The linear scale 24 cooperates with the wind direction lines 22 and the wind velocity lines 23 to indicate wind direction and wind velocity.

The flight factor side of the flight calculator is shown in Figure 4. The base ID has a window 38 through which the slidable scale member 40 is viewed. The slidable scale member 40 is mounted for sliding within the base I0 and has two linear logarithmic scales 42 and 45 which correspond to pressure altitude and indicated airspeed respectively. Adjacent the long sides of the window 38 are linear logarithmic scales 43 and 44 which correspond toair temperature and true airspeed respectively. The linear scales 43 and 44 cooperate with the linear scales 42 and 45 for performing the calculations required to convert indicated airspeed to true airspeed for variations in air temperature and pressure altitude. The stop 4| which projects up from the surface of the slidable scale member 40 serves as a means for grasping the slidable scale member 40 and also limits its movement 'in one direction by engaging one end of the base l0. 3 The cutout 38 in one end of the base I!) permits the stop 40 to engage the base ID in a position whereby the slidable scale member 40 can be completely enclosed in the base II) when not in use. The on the base I 0 serve to limit the slide assembly I 3 movement by engaging the flanged portion I! of the slide member I5. Two flat circular discs 29 and 30 are made of an opaque ma terial, mounted on the base III by means of the single pivot I 2 and have circular logarithmic scales 33 and 34 respectively, which correspond to miles or gallons and time. These logarithmic scales cooperate to; perform the calculations required to determine distance, speed, fuel consumption or fuel consumed. The top disc 30 has a hole 3| which serves as a means for easily rotating the disc 30 with respect to the disc 29 and three indices 35, 36 and 31 which correspond to units, seconds and hours or minutes respectivewhich consists of ly, for simplifying the solving of air navigation problems.

The simplicity of construction is shown in Figures 2, 3 and 5. Figure 6 shows an alternate method for obtainning a drift angle indication having an index 46 on the arm l4 and an arcuate scale 41 on the slide member I in place of the arrangement shown in Figure 1.

The mechanical calculating and computing device described above provides means for rapidly determining the essential flight factors involved in air navigation problems in a manner which is a direct carry over from the basic principles of air navigation as presented and air navigation text books. One man can readily use the device while piloting an aircraft as it can be held and operated by one hand while the other hand is free to operate the controls of the aircraft.

The operation of the flight calculator can best be described by solving typical air navigation problems. This will also indicate the importance of combining all the elements as described above in a single device.

Problem 1.Let sired The most favorable altitude for the flight is determined from a source such as the United States Weather Bureau wind aloft reports which give wind velocities, true wind directions and air temperatures at altitudes. The cruising true airspeed and fuel consumption are determined from the selected altitude and the cruising perform ance of the aircraft to be used. Let it be further assumed that the following factors were determined by the above method: Distance "miles" 2'14 True course degrees 110 Magnetic variation degrces west Pressure altitude feet 5000 Wind velocity miles per hour Wind direction degrees 220 Air temperature degrees F True airspeed miles per hour- 113 Fuel consumption gallons per hour 8 With the above factors known it now becomes The flight factors to be determined are:

Drift angle in degrees True heading in degrees Magnetic heading in degrees Ground speed in miles per hour Indicated airspeed in miles per hour Total time for the flight in hours and minutes Total fuel consumption in gallons until line is ad acent the true course index l9. Place the point corresponding to 113 miles per hour of the linear scale 24 directly over the intersection'of wind direction line corresponding to 220 and the circular wind velocity line corre by all ground schools lator as explained above).

, rotate disc 30 relati e to assaass adjacent the index 21. Thus, drift angle, true l heading, magnetic headingand ground speed have been easily predetermined by two settings on the navigation side of the flight calculator. The remaining factors must now be determined on the flight factor side as shown in Figure 4. 15.

When the cruising true airspeed is selected or determined by the selected altitude and the cruising performance of the aircraft to be used, it is necessary to determine the indicated airspeed that must be maintained to make good the selected true airspeed. The airspeed indicating instruments normally used-in aircraft measures the impact pressure of the air. For this reason the indicated airspeed reading must be correctedfor air density, that is air temperature and pressure, in order to determine the true speed of the aircraft relative to the air when conditions are other than that which the instrument is calibrated for, that is, standard sea level air temperature and atmospheric pressure This is accomplished on the flight factor side of the calculator. as shown in Figure 4 by moving the slidable scalemember 40 until 5000 foot pressure altitude line on the linear scale 42 is adjacentthe 40 Fahrenheit air temperatureJine on the linear scale" 43. Read the indicated airspeed 105 miles per hour'on the linear scale 45 adjacent the 113 miles per hour line on the linear scale H. The total time for the flight and the total fuel consumption are determined bymeans of the two flat cir- 40 cular discs 29 and 30. To determine the total time rotate disc 30 relative to disc is until the Hr. and Min. index" 37 is adjacent the 12 line on thecircular scale 38 (the12 line corresponds to 120 miles per hour ground speed determined on the navigation side of the flight calcu- Read the total time 107 minutes, or 1 hour and 4'? minutes, on the circular scale 34 adjacent the 21.4 line on the circular scale 33 (the 21.4 line corresponds to the distance from A to B of 214 miles). To determine the total fuel consumed during the flight disc 29 until the Hr. and Min. index 81 is adjacent the 80 line on the circular scale 38 (the 80 linecorrespondsto the 8 6i! gallons per hour fuel consumption determined from the performance charts of the aircraft). Read the total fuel consumed 14.3 gallons on the circular scale 33 adjacent the 107 minute line on thecircular scale 34., Thus the indicated airso speed; the total time forthe flight and the total fuel consumed during the flight have been predetermined by but one setting each on the flight factor side of the'fiight calculator.

Problem 2.Let it be assumed-that on reach ing the destination, point B, a landing could not be made due to a heavy ground fog and that it was decided to return to point A. Let it be further assumed, for simplicity, that the original weather conditions of Problem 1 still prevailed and that it was desired to fly at the same altitude and airspeed. The flight factors listed for the previous problem must again be determined as in this case the true course would be a reciprocal 1 of. the original true 'course or 1l0-i- 10=='290. to

By following the procedure given in'Problem l, thefactors determined on the navigation side of the flight calculator are: drift angle 11 rightdrift, true heading 279,magnetic heading 289 and ground speed 102 miles per hour. The factors determined on the flight factor side of the flight calculator are, total time for the flight 126 minutes, or 2 hours and 6 minutes, and total fuel consumed 16.? gallons. Thus the pilot in flight can readily determine new headings, the time and the fuel required to reach alternate flelds,'in case it becomes necessary due to unforseen conditions. This is of particular importance when the flight is conducted wholly or in part, on instruments where the pilot can not see landmarks.

Problem 3'.In the case where winds aloft are not known, a pilot can accurately determine them by conducting a check flight and using the values thus obtained to calculate the unknown factors. This is accomplished by flying at the desired altitude over land marks of known distance and known true directions, such as roads lying on section lines, accurately clocking the time for the known distance and observing the compass to determine the magnetic heading when flying a known true course. Let itbe as sumed that it was desired to fly at 5000 feet altitude, that a check flight was conducted over terrain which had roads running due north and south and due east and west being spaced at one mile intervals and that the magnetic variation existing was 10 east. Let it be further assumed that the following factors were determined on the check flight:

True course -..degrees 90 Magnetic heading -do.. Time for one mile"; seconds 50 Air temperature --degrees F... 40 Indicated airspeed ngfimiles per hour 81 In order to determine e wind velocity and direction the following factors must be calculated:

Ground speed in miles per hour True airspeed in miles per hour Magnetic course in degrees Drift angle in degrees Ground speed and true airspeed are calculated 0 from the known factors on the flight factor side of the flight calculator. Todetermine ground Jacent the 10 line on the circular scale 33 (which corresponds to one mile). Read the ground speed '12 miles per hour adjacent the Sec. index" 38. The true airspeed 8'7 miles per hour is determined in the manner described in Problem 1.

The magnetic course equals the difference between vvthe true course and the magnetic variation or 90-'10 The drift angle equals the difference between the magnetic course and the magnetic heading or 80-66=14 right drift.

With the above factors known the wind velocity and direction can be computed on the navigation side of the flight calculate This is accomplished in the following manner. Rotate the wind dial ll until 90, line is adjacent the true course index III. Move the slide assembly it until the index 21 is adjacent the line 72 on the ground speed scale 28 (which corresponds to the 72 miles per hour. ground-speed determined on the flight factor side). the driftangle-index Rotate the arm l4 until 2. is adjacent the 14 line on the right drift side of the arcuate. scale 25. Read the wind velocity miles per hour and the wind direction under the point corresponding to 87 on the linear scale 24 (which corresponds to 87 miles per hour true airspeed determined on the flight factor side of the calculator) Thus wind velocity and wind direction have been easily de-- termined and the pilot would then have suflicient information to solve problems similar to Problems 1 and 2.

Problem 4.-The mileage per gallon of fuel can be readily determined if desired by using the flight factor side of the flight calculator. Let it b assumed that a ground speed of 72 miles per hour had been determinel by the method given in Problem 3 and that a fuel consumption of 3.6 gallons per hour was known. To determine the miles per gallon, rotate the disc 30 relative to the disc 29 until the 72 line on the circular scale 33 (which corresponds to the speed '72 miles per hour) is adjacent the 36 line on the circular scale 34 (which corresponds to the fuel consumption of 3.6 gallons per hour). Read the mileage 20 miles per gallon on the circular scale 33 adjacent the "unit index" 35.

It is readily apparent from the above problem that the flight calculator described will be of considerable aid to all persons who must be familiar with air navigation problems and particularly to-the pilot who must be his own navigator while he is flying an aircraft.

I claim:

1. A flight calculating device which comprises an elongated rectangular base member, a graduated disc member and a slidable assembly, said base member having a linear scale corresponding to ground speed, an arcuate scale corresponding to drift and variation and an index for indicating the true course, said arcuate drift and variation scale and said true course index being adjacent one end of said base member, said disc member being pivotally mounted on said base member and having a graduated scale on the periphery corresponding to a compass rose, radial lines corresponding to wind direction and concentric circular lines corresponding to wind velocity, said graduated scale being in registration with said arcuate scale, said slidable assembly mounted on said base member for sliding thereon comprising a slide member and an arm pivoted thereto, said slide member having a portion extending-across the face of the base member and having flanged edge engaging portions to engage the edges of said base member to slide thereon and having an index for indicating ground speed, one end of said arms overlapping said disc member and having a linear scale corresponding to true'airspeed, the other end of the said arm and said slide member having cooperating elements, one of said elements being an arcuate scale corresponding to drift angle,

the other element being .an index for indicating drift angle, said members, scales and indices cooperating whereby the unknown factors of air navigation may be determined bythe proper setting of the known factors.

2. The device set forth in claim 1', having said around speed scale parallel to the. center line oi. said base member and cooperating with said ground speed index, said linear true air speed scale originating at the center of said arm pivot, said arcuate drift scale having center oi arc in common with center of said arm pivot, said arcuate wind drift scale and said drift angle index a being positioned symmetrically of a straight line connecting the center of said arm pivot and center of disc pivot in their. zero relation.

3. In a flight calculator of the character described, the combination consisting of an elongated base member having a set of ground speed graduations extending longitudinally thereof, a centrally pivoted disc mounted on said base member adjacent one of its ends and having radial graduations corresponding to wind direction extending through 360 degrees with subdividing concentric circles corresponding to wind velocity, said base member having also an indicator thereon in cooperative relation to the outermost edge portion of said pivoted disc, a slide member constrained to move longitudinally of said base member and having an indicator thereon disposed for cooperation with the ground speed graduations of said base member, and an extended arm pivotally connected intermediate its ends to said slide member at a point determined by the intersection of perpendicular lines extending respectively from the pivot point of said pivoted disc and at right angles to the set of ground speed graduations, one end of said extended arm having a transparent portion overlying said pivoted disc and provided with a set of true air speed graduations radially aligned with its point of pivotal connection, and the other end of said extended arm and the adjacent portion of said slide member being provided with relatively movable drift angle arc graduations and index means which are respectively concentric and radial with respect to the point of pivotal connection of said extended arm.

4. In a wind triangle calculator of the character described, the combination consisting of an elongated base member having a set of ground speed graduations extending longitudinally thereof, a centrally pivoted disc mounted on said base member adjacent one of its ends, with its-periphand magnetic compass variation, a slide member constrained to move longitudinally of said base member and having an indicator thereon disposed for cooperation with the ground speed graduations of said base member, and an extended arm pivotally connected intermediate its ends to said slide member at a point determined by the intersection of perpendicular lines extending respectively from the pivot point of said pivoted disc and at right angles to the set of ground speed graduations, one end of said extended arm having a transparent portion overlying said pivoted disc and provided with a set of true air speed graduations originating with its point 01' pivotal connection, and the other end of said extended arm and the adjacent portion of said slide member being provided with relatively movable drift angle arc graduations and index means which are respectively concentric and radial with respect to the point of pivotal connection of said extended arm.

5. In a wind triangle calculator of the character described, the combination consisting of an elongated base member having a set-of ground weed graduations extending longitudinally thereof, a centrally pivoted disc mounted on said base member adjacent one of its ends, with its periphery spaced from that end, and having .radial graduations corresponding to wind direction extending through 360 degrees withtsubdividing concentric circles corresponding to wind velocity, and said base member having also an indicator thereon in cooperative relation to the outermost edge portion of said pivoted disc, a slide member constrained to move longitudinally of said base member and having an indicator thereon disposed for cooperation with the ground speed graduations of said base member, and an extended rectilinear arm pivotally connected intermediate its ends to said slide member at a point determined by the intersection of perpendicular iines extending respectively from the pivot point said pivoted disc and at right angles to the set of ground speed graduations, one end of said extended arm having a transparent portion over lying said pivoted disc and provided with a set of true air speed graduations originating with its point of pivotal connection, and theother end or said extended arm and the adjacent portion of said slide member being provided with relatively movable drift angle arc graduations and index means which are respectively concentric and radial with respect to the point of pivotal connection of said extended arm.

6. In a wind triangle calculator of the character described, the combination consisting of an elongated base member having a set of ground speed graduations extending longitudinally thereof, a centrally pivoted disc mounted on said base member adjacent one of its ends, with its periphery spaced from that end, and said disc having radial graduations corresponding to wind direction extending through 360 degrees with subdividi ng concentric circles corresponding to wind velocity, said base member having also an indicator thereon in cooperative relation to the outermost edge portion of said pivoted disc and flanked on each'side by graduated scales forming continuations of the opposed radial graduations of said disc and corresponding to both wind drift and magnetic compass variation, a slide member constrained to move longitudinally of said base member and having an indicator thereon disposed for cooperation with the ground speed graduations of said base member, and an ex tended arm pivotally connected intermediate its ends to said slide member at a point determined by the intersection of perpendicular lines e:;- tending respectively from the pivot point of said pivoted disc and 'at right angles to the set of ground speed graduations, one end of said ex tended arm having a transparent portion overlying said pivoted disc and provided with a set of true air speed graduatiohs originating with its point of pivotal connection, and the other end of said extended arm and the adjacent portion of said slide'member being provided with relatively movable drift angle arc graduations and index means which are respectively concentric and radial with respect to the point of pivotal connection of said extended arm.

EVERT CARL HOKAN SON. 

